Numerous devices are currently available to attach objects to bone. More specifically, screws, staples, cement and sutures have all been used to attach soft tissue (e.g. ligaments, tendons, muscles, etc.), bone and inanimate objects (e.g. prostheses) to bone. Unfortunately, all of the foregoing attachment devices tend to suffer from one or more serious disadvantages.
Screws suffer from the disadvantage that they tend to loosen with time, thereby requiring a second operation to remove the loosened screw. In addition, when the screws are set in bone, the heads of the screws frequently protrude above the surface of the bone in which they are set, thereby presenting an abrasive surface which may create wear problems with surrounding tissue. Also, properly fastening the screws into bone can be time-consuming, since a pilot hole must normally be drilled into the bone and then, depending on the bone structure, the bone may also have to be tapped to accept the screw. Furthermore, once the pilot hole has been drilled, the position of the screw is then determined so that it is impossible to thereafter alter the position of the screw or to adjust the degree of tension being applied to the object which is being attached to the bone without drilling a new hole. Also, once a hole has been made in the bone it may be impossible to relocate the hole a small distance away from its original position due to the disruption of the bone structure created by the initial hole. Finally, the nature of a screw attachment tends to require a flat attachment geometry; the pilot hole must generally be located on a relatively flat section of the bone, and toothed washers must frequently be used in conjunction with the screws to fasten the desired objects to the target bone. As a result of these constraints, it may be necessary to locate the attachment point at a less than optimal position.
Staples suffer from their own set of disadvantages. More particularly, bone staples must frequently be removed after they have been in position for some time, thereby necessitating a second operation. In addition, staples must generally be positioned so as to maximize their holding power in the bone; such positioning may conflict with the otherwise-optimal position for attachment of the objects to bone. Staples have also been known to crack the bone during deployment, or to accidentally transect the object (e.g. soft tissue) being attached to the bone, since it tends to be difficult to precisely control the extent of the staple's penetration into the bone. Finally, as is the case with screws, once the staple has been set into the bone the position of the staple is then effectively determined, thereby making it impossible to thereafter adjust the position of the staple or to adjust the degree of tension being applied to the object which is being attached to the bone without setting a new staple.
Cement can be a better solution than screws or staples where an object is being attached to the interior portion of the bone, e.g. as in the case of a total hip replacement, but it is generally unsatisfactory where an object must be attached to the exterior surface of the bone. The use of cement can also raise problems relating to setting time, part immobilization during setting time, and substance compatibility with body tissues.
The use of sutures to attach objects to bone is accompanied by a different, but no less troublesome, set of problems. Sutures generally require that holes be drilled in the bone prior to suturing so that the sutures can be passed through the holes in the course of attaching objects to the bone. Drilling these suture-receiving holes in the bone can be time-consuming; in addition, since the sutures which are used to attach objects to the bone are generally quite thin (e.g. 0.020 inches) and since the load imposed on the sutures is generally quite sizable, the sutures have been know to pull completely through the bone, thereby failing as an attachment device and possibly seriously damaging the bone as well.